HP HDD BackPane kit

PartNo: 445985-B21ManualRev: Sept 2007 (First Edition)

Im running a DL160G5 server with the hdd backplane described as above.But is was wondering what use part: 450219-001/SpareNo: 452337-001 is for?i also have 2 hdd hot-swap brackets attached to it, and no leds are working.

in the manual it states: 'Header for backplane aligns to backplane inter-connection'so to be short, and to the point: